Abstract Long term administration of nonsteroidal anti-inflammatory drugs (NSAIDs) can significantly reduce the risk of death from colorectal cancer. Unfortunately, toxicity resulting from cyclooxygenase (COX) inhibition and incomplete protection from disease progression in all individuals, limits their use for chemoprevention. Previous studies suggest that COX inhibition is not required for the antineoplastic activity of NSAIDs, which led us to hypothesize that it may be feasible to develop safer and more effective derivatives by designing out the COX inhibitory activity, while enhancing anticancer selectivity. To develop this approach, we used molecular modeling to identify specific chemical properties of the NSAID, sulindac sulfide (SS) that are crucial for COX-1 and COX-2 binding. These studies demonstrated the importance of the carboxylic acid moiety and suggested a strategy to selectively disrupt COX binding. From a series of derivatives that were synthesized and screened, a novel compound referred to as sulindac sulfide amide (SSA) was identified that potently inhibits colon tumor cell proliferation (IC50 = 1mM), selectively induces apoptosis of colon tumor cells, and inhibits angiogenesis, despite lacking COX-1 or COX-2 inhibitory activity. SSA has desirable in vivo pharmacological properties and was well tolerated in mice, although has limited oral bioavailability, which requires high dosages for in vivo antitumor efficacy. Nonetheless, the administration of SSA by the diet significantly inhibited colon tumor formation in the FCCC Min mouse model by greater than 80%. To develop a formulation of SSA with improved oral bioavailability, we found that the commercially available antacid, Maalox(R) can appreciably enhance absorption and antitumor efficacy of SSA in the HT-29 xenograft mouse model. Here we propose to optimize a formulation for SSA that will result in a high level of chemopreventive efficacy (Aim 1). This formulation of SSA will then be evaluated for efficacy and toxicity in a comprehensive manner using the FCCC Min mouse model (Aim 2). In Aim 3, the molecular target of SSA will be studied by identifying sensitive and resistant cell lines to SSA that will be used for photo-affinity labeling and whole genome microarray analysis. In vitro and in vivo treatment effects of SSA on the expression of putative targets will also be determined as well as potential differences with regard to tumorigenesis. The proposed studies will determine if SSA is a clinical candidate for colorectal cancer chemoprevention and will investigate the molecular targets responsible for its antineoplastic activity that we suspect may also be involved in colon tumorigenesis.